1. Field of the Invention
This process relates to a method of decreasing the elemental phosphorus (P.sub.4) levels in an aqueous medium, and more particularly, an aqueous medium which is the liquid waste effluent from the electric furnace process for preparing elemental phosphorus.
2. Prior Art
In the electric furnace process for preparing phosphorus phosphate-bearing ore, rock or earth is charged to an electric furnace with silica and carbon, usually in the form of coke or coal. The electric furnace is heated to a sufficient temperature to melt the charge. The phosphorus generated is removed as a vapor with carbon monoxide gas. This vapor, however, as it leaves the furnace, entrains minute particles of carbon, phosphate rock and other materials present in the furnace. This phorphorus-containing gas stream is generally passed into a hot gas precipitator which removes a large portion of the entrained solids. The stream is then passed through a hood type condensor before it is exhausted through a spray tower.
Thus, a major portion of the phosphorus vapor is condensed by cooling with water. The greater proportion of this condensed phosphorus separates and is filtered to remove residual dirt particles. The phosphorus is collected and stored under water for it is combustible when exposed to air.
The liquid waste effluent from this process is called "phossy" water. The phossy water contains small quantities of elemental phosphorus (P.sub.4) and after some initial processing by, for example, coagulation, neutralization and clarification, the resulting aqueous liquid may contain from about 10 ppm to about 3 ppm of elemental phosphorus.
Phosphorus has been found to be particularly toxic to aquatic life, especially fish. Thus from an environmental protection point of view, the discharge of phossy water to aquatic life bearing water bodies should be avoided. It has been reported, that autopsies on fish killed by elemental phosphorus poisoning discloses the nearly complete disintegration of blood cells by homolysis. Studies have shown that fish are extremely sensitive to elemental phosphorus.
It is therefore desirable to reduce the elemental phosphorus (P.sub.4) content of the phossy water from, say about 10 ppm, to only a few parts per billion, e.g. less than 5 ppb.
Due to the colloidal nature of the suspension of the elemental phosphorus in the aqueous medium, it is extremely difficult to separate out the solid elemental phosphorus by physical methods, such as filtration and centrifuging. In addition, simple dilution of this waste effluent is ineffective since the elemental phosphorus tends to accumulate at the discharge point of the waste water rather than be dispersed.
The present invention makes it possible to decrease the elemental phosphorus content of an aqueous medium below a level of, for example, 5 ppb and hence allow the safe discharge of the treated aqueous medium to water bodies or to storage where water seepage may find its way into aquatic life bearing water bodies.
U.S. Pat. No. 3,971,707 to Deshpande attempts to solve the aforementioned problem by electrolysis. Needless to say, this process requires complicated and expensive equipment.
In the past, phossy water has been treated with calcium hydroxide, lime, etc. Such treatments, however, were generally performed at low pH and thus did not achieve the dramatic results achieved by this invention. See, for example, the following references:
Phosphorus and Its Compounds, Van Wazer, John R. (1961), Vol. II p. 1204-1205; PA1 Direct Determination of Elemental Phosphorus By Gas-Liquid Chromatography, Ackerman et al. Proc. Chem. Inst. of Canada. Polln. Conf., Halifax, August 1969, pp. 140-147; PA1 Coexistence of a Fishery and a Major Industry In Plancentia Bay, Newfoundland, Proc. Chem. Inst. Canada Polln. Conf., Halifax, August 1969, pp. 5-15; PA1 Waste Control In a Fragile Environment, Environ. Science and Tech. V., 6, 980 (1972); PA1 U.S. Pat. No. 3,971,707, Deshpande, Erco Industries Ltd., Issued July 27, 1976.